Excited-State Geometry Optimization with the Density Matrix Renormalization Group, as Applied to Polyenes

We describe and extend the formalism of state-specific analytic density matrix renormalization group (DMRG) energy gradients, first used by Liu et al. [<i>J. Chem. Theor. Comput</i>. <b>2013</b>, <i>9</i>, 4462]. We introduce a DMRG wave function maximum overlap following technique to facilitate state-specific DMRG excited-state optimization. Using DMRG configuration interaction (DMRG-CI) gradients, we relax the low-lying singlet states of a series of <i>trans</i>-polyenes up to C₂₀H₂₂. Using the relaxed excited-state geometries, as well as correlation functions, we elucidate the exciton, soliton, and bimagnon (“single-fission”) character of the excited states, and find evidence for a planar conical intersection